1. Field of the Invention
The present invention relates to an offset measurement method for a magnetic recording head and a magnetic recording/reproducing device for controlling the positioning of a magnetic head on a magnetic recording medium where a non-magnetic area is created between magnetic recording tracks, such as a patterned media, and more particularly to an offset measurement method for a magnetic recording head and a magnetic recording/reproducing device for controlling the positioning of a magnetic head, where the reproducing element and recording element are separated, on the magnetic recording medium.
2. Description of the Related Art
In a magnetic disk device, accurately positioning a magnetic head to a target track is extremely important to improve recording density. For a magnetic head of this magnetic disk device, a separate type head in which a reproducing element and recording element are separated is used.
In the separate type head, where the reproducing element and recording element are separated, it is difficult to make the positions of these elements perfectly the same in manufacturing, so the positions of these elements are different. Therefore in order to position the reproducing element and recording element of the separate type head on a track, the positional shift of these elements (offset) must be measured, and according to the measured offset, the recording element of the magnetic head is positioned on a track during write, and the reproducing element of the magnetic head is position on a track during read.
For a magnetic disk device, discrete tracks and patterned media are proposed, other than a conventional disk where a magnetic layer is formed on the entire disk face. FIGS. 20A, 20B and 20C are diagrams depicting the discrete track media and patterned media. As the cross-sectional views of the disks in FIGS. 20A, 20B and 20C show, these disks have tracks which are recording areas, and unrecordable areas are arranged alternately in the radius direction.
For example, in the case of the discrete media in FIGS. 20A and 20B, grooves 301 are formed on the disk substrate 340 with a predetermined space, and the magnetic layer is formed on the entire surface. In FIG. 20A, filler is also formed in the grooves 301. Then the tracks 302, which are recording areas having a magnetic layer on the surface, and a recording disabled area 301 which consists of grooves, are arranged alternately in the radius direction.
Further, in the case of the patterned media in FIG. 20C, a magnetic layer is formed on the disk substrate 304 via a mask used in semiconductors. Then the tracks 302, which are recording areas having a magnetic layer on the surface, and a recording disabled area 301 not having the magnetic layer, are arranged alternately in the radius direction.
Creating a recording disabled area between tracks guarantees the recording contents of each track without receiving the influence of writing on an adjacent track, therefore this is effective to increasing the density of tracks. Particularly this method is effective to prevent influence on an adjacent track due to the side fringing of the recording head of vertical magnetic recording. In the case of this type of disk, on which the recording areas and non-recording areas are alternately arranged, the data tracks 302 are formed in advance, and it is impossible to change the positions later.
Therefore a problem of the device which uses this type of disk is follow up control to the data tracks. For follow up control, measuring the above mentioned offset and follow up control using the offset are required.
FIG. 21 is a diagram depicting a conventional offset measurement method. In the magnetic disk device, of which read element and write element are different, offset between these elements is measured for each position in the radius direction. This offset is measured assuming that the magnetic film is continuously formed in the radius direction.
The servo area 320 is formed even for the discrete track medium. In the servo area 320, however, the servo information is formed by magnetic recording or by pit shaped patterns, separately from the data tracks 302, so error “A” is generated between the position of the data track 302 and the position indicated by the servo information 320.
Possible causes of this error are a position error when servo signals are formed and a position error when data tracks are formed. Generation of an error is inevitable whether a mask equivalent to a semiconductor mask is used or signals are recorded, since ultimately the data is mechanically recorded. While the precision required is at the nanometer level, a position error cannot be suppressed until it becomes negligibly small.
In discrete tracks and pattern media, magnetic films are discontinuously formed in the radius direction. Therefore a correction method different from the disk having a continuous magnetic layer is required.
As FIG. 21 shows, in the conventional proposal, it is assumed that the shift amount “A” between the center C1 of the servo information 320 and the center C2 of the track 302 is constant in each track. And the measurement area 310 is formed between the data area 300, on which the data tracks 302 and non-recording areas 301 are formed, and the servo area 320. The recording element 331 or reproducing element 332 of the magnetic head 330 is placed at the track center in the measurement area 310, and the measurement data is recorded by the recording element 331 and the measurement data is read by the reproducing element 332.
Also while shifting only one of the recording position and reproducing position, recording or reproducing is repeated and the position at which the signal quality peaks is searched, and offset due to the position shift “B” between the recording element 331 and reproducing element 332 is measured as a relative position of the recording element 331 and reproducing element 332 (e.g. Japanese Patent Application Laid-Open No. 2005-166115 and No. 2005-166116).
According to these proposals, the recording element 331 may record measurement data for two tracks 302 when offset is measured, depending on the shift between the servo center C1 and the data track C2, so the offset is measured by creating the measurement area 310 between the data area 300 and the servo area 320.
However because of the recent demand for larger capacities of magnetic disk devices, an increase in the data recording density is required. For this, track density must be increased even in discrete type disks. If the track density is increased, the shift amount A between the center C2 of the data track 302 and the center C1 of the servo information 320 is unknown and differs depending on each disk.
Also the position shift “B” between the recording element and reproducing element of the magnetic head is at the nana level as magnetic heads miniaturize, and producing a magnetic head where this shift “B” is constant is difficult, and also the core width differs between the recording element and reproducing element. Distribution of the signal quality level changes depending on the core widths of the recording element and reproducing element.
Therefore in the prior art, which firstly assumed that the shift amount “A” between the center C2 of the data track 302 and the center C1 of the servo information 320 is known and constant, an offset of a disk in which the shift amount “A” is unknown cannot be measured accurately.
Also in the prior art, a position where the maximum values of signal quality, such as amplitude, S/N ratio and error rate of written signals, is measured as one offset position. However the distribution of the signal quality level changes depending on the widths of the reproducing element and recording element, so the area where the maximum values of the signal quality must be measured more than at one point, so accurate offset measurement is difficult.